1. Technical Field
This disclosure relates generally to hydraulic fracturing and more particularly to systems and methods for improving efficiency of turbine generator operation in order to supply electric power to all components of the hydraulic fracturing operation.
2. Background
With advancements in technology over the past few decades, the ability to reach unconventional sources of hydrocarbons has tremendously increased. Horizontal drilling and hydraulic fracturing are two such ways that new developments in technology have led to hydrocarbon production from previously unreachable shale formations. Hydraulic fracturing (fracturing) operations typically require powering numerous components in order to recover oil and gas resources from the ground. For example, hydraulic fracturing usually includes pumps that inject fracturing fluid down the wellbore, blenders that mix proppant into the fluid, cranes, wireline units, and many other components that all must perform different functions to carry out fracturing operations.
Usually in fracturing systems, the fracturing equipment runs on diesel motors or by other internal combustion engines. Such engines may be very powerful, but have certain disadvantages. Diesel is more expensive, is less environmentally friendly, less safe, and heavier to transport than natural gas. For example, diesel engines are very heavy, and so require the use of a large amount of heavy equipment, including trailers and trucks, to transport the engines to and from a wellsite. In addition, such engines are not clean, generating large amounts of exhaust and pollutants that may cause environmental hazards, and are extremely loud, among other problems. Onsite refueling, especially during operations, presents increased risks of fuel leaks, fires, and other accidents. The large amounts of diesel fuel needed to power traditional fracturing operations require constant transportation and delivery by diesel tankers onto the well site, resulting in significant carbon dioxide emissions.
Some systems have tried to eliminate partial reliance on diesel by creating bi-fuel systems. These systems blend natural gas and diesel, but have not been very successful. It is thus desirable that a natural gas powered fracturing system be used in order to improve safety, save costs, and provide benefits to the environment over diesel powered systems. Turbine use is well known as a power source, but is not typically employed for powering mobile fracturing operations.
Though less expensive to operate, safer, and more environmentally friendly, turbine generators come with their own limitations and difficulties as well. In hot climates with high ambient temperatures in particular, turbine operation efficiency may be compromised. For example, a fleet of turbine equipment with three Taurus 60 generators may be rated to produce 17.1 megawatts (MW) of electricity during normal operating conditions at approximately 55 degrees Fahrenheit. In the summer, when temperatures may reach up to 100 degrees Fahrenheit, and with further power losses from cables, breakers, switchgear, and transformers, the electrical power supply capacity may be below 14.7 MW of electrical power, which is the minimum power required to operate the equipment in accordance with a particular application of fracturing equipment at a well site. Failure to meet the required pump rate against wellhead pressure may result in unsatisfactory well stimulation.
Thus, it may be desirable to modify turbine operation in order to mitigate losses in efficiency, and particularly losses caused by high ambient temperatures.